Marching operations for a large number of workpieces require the sequential use of several tools on the same workpiece in accordance with a previously decided and automatically controlled cycle.
The workpiece is normally mounted for this purpose on the lathe which comprises a turret bearing a plurality of tools which can be disposed when necessary in the operating position to perform the machining of the workpiece required from them under the control of an electronic unit.
A fundamental requirement of such machining is speed, in particular by reducing the idle time between the end of machining by one tool and the beginning of machining by the next tool needed to allow the turret to perform all the movements required to bring the new tool into the operating position.
For this purpose the turret must unlock from the fixed operating position, rotate in one or other direction along the shortest path until the new tool is located in the operating position, stop and return to the locked position.
These operations are carried out, in known turrets, by mechanical devices which transmit the rotation from a drive motor to the too-holder plate and simultaneously control the actuation of the locking and unlocking means, using particularly complex and costly structures.
The German Patent DE 31 34 969 in the name of SAUTER FEINMECHANIK GmbH discloses a turret in which a motor causes, via a reduction gear of the epicyclic type, the rotation of a ring bearing rollers which cause, via cam openings of a locking ring, the axial movement of the locking ring itself, which rotates together with the tool holder plate, causing the unlocking of the tool holder plate; the subsequent rotation of the ring bearing the roller drives, via correspondingly shaped recesses within which the rollers are engaged, the tool holder plate; when the desired position is reached and the rotation of the tool holder plate is arrested, the subsequent reverse rotation of the motor causes, via the cam openings, the locking ring to return to the locked position.
The Italian Patent No. 1138598 in the name of DUPLOMATIC APPLICATION OLEODINAMICHE has a motor which drives, via a worm screw and helical gear reduction unit, an assembly provided with rollers engaged with the cam profile of a slide coaxial therewith, rigid with a locking ring of the tool holder member and connected thereto in rotation; the rotation of the assembly firstly causes the axial movement of the slider, thus unlocking the tool holder and then, after unlocking, the drive of the slider and the tool holder into the desired position where, after the tool holder is arrested, a rotation of the assembly in the opposite direction brings the slider back into the locking position.
In both these embodiments the locking member of the tool holder is caused to rotate together with this holder as well as performing an axial movement for the locking and unlocking of the tool holder.